Games with mod/level editor support

Do you like games that give you that little extra thing to mess with when you're bored of the main game? Have a look at these then!

(If there's a game that you know has good mod support that's not here, it probably means I haven't played it and therefore can't really judge its modability that well, so my bad)

(Also, reccomendations are mostly based on how easy it is to mod said game from the perspective of actually modding it, not making mods for it, and are not neccesarily indicative of what I think of the actual game. But you'll probably yell at me anyway.)

(icon from a free icon website cause i'm a talentless hack)